1. Field
The present disclosure relates to a method and a device for fabricating three-dimensional objects with improved properties by successive consolidation, layer by layer, of the areas selected from a layer of material in powder form, the consolidated regions corresponding to successive sections of the three-dimensional object. Such a fabrication method, also known under the name of powder-based additive fabrication, forms partially or totally, layer by layer, a sintering or a fusion of the grains of powder using electromagnetic radiation (for example a laser beam) or a beam of particles (for example an electron beam).
2. Description of Related Art
One example of a device for producing a three-dimensional object layer by layer starting from a material in powder form by selective fusion of powder using a laser beam is known from the document U.S. Pat. No. 4,863,538. The document WO 0181031 describes a device for fabricating a three-dimensional object by a powder-based additive fabrication method which uses an electron beam. The objects obtained generally have complex shapes and exhibit a reasonably good geometrical precision. However, depending on their use, these objects must sometimes undergo additional operations which are aimed at improving their resistance to wear, to fatigue or to the mechanical stresses to which they are subjected.
The objects fabricated must satisfy the conditions of operation or of use, notably by exhibiting a good resistance to the various mechanical stresses. The mechanical properties of a component can vary depending on the geometry of the component and on the type of stresses to which it is subjected. Thus, a component must, for example, exhibit high-strength mechanical characteristics over regions of limited extent, on the surface, whereas the bulk of the component must exhibit a high ductility. These mechanical properties are obtained by subjecting the component to a heat treatment.
The mechanical stability of the surface is important notably when the objects fabricated must exhibit a good resistance to fatigue or to wear. In general, the mechanical properties of resistance to fatigue or to wear of the objects fabricated are improved by surface heat treatments. Surface heat treatments most frequently use heat treatment installations comprising induction devices. However, the treatment carried out with these installations can cause deformations within the treated components. It has furthermore been observed that, for the objects with complex geometric shapes, the desired parameters for the heat treatment could not be ensured in all the sections of the object using conventional treatment methods.
In order to overcome these drawbacks, it is also known for the surface treatment of the objects to be applied by means of high energy density beams, such as laser beams or electron beams. These treatments are more particularly suited to components having complex geometries, such as the majority of components obtained by powder-based additive fabrication methods.
The document DE 100 07 962 describes such a powder-based additive fabrication method which uses a laser beam in order to solidify the grains of powder, layer by layer, so as to obtain an injection molding element. The component obtained has a high roughness and, for this reason, its surface is subsequently subjected to a surface finishing operation carried out by means of a second laser beam which effects a surface fusion of certain regions of its surface in order to reduce its roughness. The use of the second laser beam in this document is limited to a superficial fusion of the finished component.
The document WO 02/11928 describes a method for obtaining precision components by a method for additive fabrication based on a mixture of powders, using a laser beam, the component being subsequently subjected to heat treatments. The heat treatments described are aimed at rendering the structure uniform, at relieving the internal stresses, at eliminating the defects or at improving the surface condition. These treatments are carried out by subjecting the component obtained to an additional sintering then a slow cooling cycle in an oven. This assumes the implementation of separate treatment means that are remote from those of the fabrication, which implies that a treated component is obtained after a long period of time, in view of the quite long treatment times to which are added the time for transferring the components between the fabrication station and that for the treatment.
The document DE 10 2007 059 865 describes another method for obtaining a metal component by a powder-based additive fabrication method using a laser beam. According to this document, the metallographic properties of the component are locally modified within the component thus obtained by a reheating of the molten region by means of an element heating by infrared radiation or by means of a laser beam. An improvement in the hardness, in the tenacity or in the resistance of the component is thus obtained. This document has the main drawback of the length of time needed to obtain the component, notably when the same laser is used firstly for solidifying and subsequently for performing the heat treatment of the latter.
From the document U.S. Patent No. 2011/0165339, a method and a device are furthermore known for fabricating three-dimensional objects which are at least in part composed of a composite of crystalline metal within a matrix of amorphous metal. Such an object is formed by depositing a material in powder form, layer by layer, which deposition is followed by a local solidification of this material by fusion with a laser beam or with an electron beam and by a controlled cooling of the fused region. The power of the source and the speed of travel of the beam over an area of limited dimensions of the layer of powder are chosen in such a manner that by varying the speed of cooling of the treated area, the latter can adopt a crystalline or amorphous structure. The device described in this document employs a single source of energy whose emitted beam treats very small regions, while often changing position, a fact which lengthens the fabrication time for a component. For this reason, this device is not suitable for the fabrication of components with medium or large dimensions, nor for high-volume manufacturing.